This application claims the priority of Japanese application 8-341490, the disclosure of which is expressly incorporated by reference herein.
1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus which is able to record and reproduce a signal from an image sensor such as a CCD, as well as a composite video signal, in particular, to the magnetic recording/reproducing apparatus equipped with such the image sensor formed or constructed as an unit, in which a camera portion and a video signal processing portion thereof are realized by digital signal processing circuits.
2. Description of the Related Art
Almost of video signal processing in a conventional VTR set of stationary type for home use and a portable VTR equipped with a camera formed or constructed as an unit, such as so-called a camcorder, is constructed with a signal processing circuit for an analogue signal processing. However, with a VTR under the S-VHS standard and/or a camcorder under the Hi8 standard which are already available on the market, the signal processing circuit thereof is constructed with a digital signal processing circuit.
Especially, for the case of the camcorder, a system is proposed, in which an A/D converter is commonly used by sharing with a digital processor of the camera portion (hereinafter, xe2x80x9ca camera DSPxe2x80x9d) and a digital processor of the VTR portion (hereinafter, xe2x80x9ca video DSPxe2x80x9d) thereof, for example in Japanese Patent Laying Open No. 8-51565 (1996). In this case, for decreasing the number of pins of the IC of the A/D converter, three kinds of input signals, i.e., a camera signal from the camera system, a video signal from a line input terminal, and a reproduced video signal from a VTR system, are inputted to the A/D converter for common use after being selected through a change-over switch, and a digital signal outputted therefrom is distributed through another change-over switch. Further, an interface circuit is provided for compensating level differences occurred during this period among those three kinds of signals.
Inventors of the present invention acknowledged following problems with respect to the prior art mentioned in the above publication (i.e., Japanese Patent Laying Open No. 8-51565 (1996)).
First of all, the reproduced signal inputted into the A/D converter is the video signal which has been treated with FM demodulation, therefore, an analogue processing circuitry is still necessary for the part of signals up to the demodulation. Namely, there are mixed the digital circuit and the analogue circuit in the circuitry for processing the video signal in the VTR portion, therefore being complex in the structure.
Further, in case of sharing the A/D converter in common with the camera DSP and the video DSP, a new technology with respect to the video signal processing is necessary, however, there is no disclosure about it in that publication.
The object of the present invention, in accordance with the present invention, is to provide a low price magnetic recording/reproducing apparatus and the same equipped with an image sensor as an unit, with which the video signal can be processed more suitably when sharing the A/D converter in common with the camera DSP and the video DSP.
When processing the reproduced FM signal (before demodulation) from the magnetic head by converting it into a digital signal, comparing with the signal from the image pick-up element which is converted from an analogue into a digital signal and processed by the camera DSP, and with a signal which is obtained by A/D conversion of an external input signal (the composite video signal), there are difference in sampling frequency due to frequency band of signals. Therefore, the sampling frequencies are different due to the difference in frequency bands of the signals and the difference lies between the camera processing and the VTR processing. Those cannot be dissolved only by compensating the level differences among those signals.
Further, with a performance that is necessary for the A/D converter used in the conventional camera DSP, it must operate at a sampling clock around at 4 fsc (here, fsc: a frequency of color sub-carrier, and 14.3 MHz, for example, in a case of NTSC set), and it must have 9 through 10 in the bits number thereof. Consequently, such the A/D converter which is used in those has the maximum about 15 MHz through 20 MHz in the sampling frequency. On the contrary to this, with the video DSP, since it treats with the reproduced FM signal of wide frequency band, it cannot satisfy a theorem necessary for sampling with such the sampling clock at 4 fsc (14.3 MHz) mentioned above, and necessitates a sampling clock higher than that. On the other hand, ordinarily the clock signal of 4 fsc is used for processing of the video signal after the FM demodulation, and as for dealing with this case, it is easy and common technique to set the clock at 8 fsc (28.6 MHz) two times higher than it with respect to the FM signal. Namely, by using the A/D converter of 30 MHz class in the maximum sampling frequency, the video DSP circuit can be simplified in the structure, on the contrary, it means that a very expensive A/D converter is used therein, therefore, it is not in conformity with an object of the present invention.
In accordance with the present invention, it is an object to provide a magnetic recording/reproducing apparatus having a low price signal processing circuit, by using the A/D converter of performance less than 20 MHz which has been conventionally used in the camera DPS as the A/D converter, in which a clock signal of an appropriate sampling frequency is supplied to the A/D converter in each of operation modes, i.e., a mode of camera recording, a mode of external input recording, and a mode of reproducing, and in particular in the reproducing mode, after completing the sampling by the available maximum frequency thereof, the reproducing process is carried out by exchanging or converting the clock rate to a system clock frequency which is used for video signal processing.
Further, a main function of the camera DSP is of receiving and outputting signals from and to the image sensor, then it is difficult to maintain synchronization with the video DSP. For dealing with this, in accordance with the present invention, in the operation of the video DSP, the signal is processed by using the clock of the camera DSP in the camera mode, while it is processed by using the system clock which is generated within the video DSP in the external inputting mode. Namely, the signal processing comes to be easy between those two DSPs which are in the synchronization, by exchanging or converting between the clock from the camera DSP and the system clock generated within the video DSP.
Furthermore, in accordance with the present invention, it is assumed that the sampling rate of the camera DSP is exchanged depending on the number of the picture elements or pixels of various kinds of the image sensors. In the case that the sampling rate of the camera DSP differs greatly from that of the video DSP, it becomes more difficult to process the video signals therewith. As a method for dissolving such the problem, in accordance with the present invention, there is provided a low price magnetic recording/reproducing apparatus with an image sensor, in which the clocks are unified as an original one clock signal for common use in both the camera DSP and the video DSP, so as to keep the two DSPs in synchronism basically, and then the sampling rate, which is variable depending on the number of the picture elements of the image pick-up element, is compensated at the side of the video DSP in the camera recording mode, thereby making the signal processing in common after the compensation, and simplifying the signal processing in the video DSP.